Composite flexible hoses used for transporting refrigerant gases for vehicle air conditioners and refrigerant gases for freezer or refrigerator vehicles are required not only to have gas barrier properties and flexibility for restraining the permeation of refrigerant gas but also to resist an external pressure and an internal pressure of the transported gas. An example of such composite flexible hoses is recited in Patent Literature 1.
As shown in FIG. 3, a composite flexible hose 101 of Patent Literature 1 is formed by laminating, from the inner side, an innermost layer 102, an intermediate rubber layer 103, a fiber reinforcement layer 104, and an external rubber layer 105 in this order. Because the innermost layer 102 is made of polyamide resin, gas barrier properties are obtained. Furthermore, because the intermediate rubber layer 103 is made of halogenated butyl rubber, not only flexibility but also gas barrier properties and water barrier properties are obtained.
In so-called eco cars such as hybrid vehicles and electric vehicles, an electric compressor is mounted as an air conditioner system. It is necessary in the electric compressor to electrically insulating an internal motor from a housing, and polyol ester (POE) which excels in electric insulation is used as lubricating oil for the electric compressor. To maintain this electric insulation, it is necessary to restrain the entrance (permeation) of water into the air conditioner system as much as possible. For this reason, a hose used for transporting refrigerants for such an air conditioner system is also required to restrain the permeation of water from the outside as much as possible, i.e., required to have better water barrier properties.
In the case of the composite flexible hose of Patent Literature 1, however, into the intermediate rubber layer 103 (made of butyl rubber) for obtaining water barrier properties, an adhesive component is kneaded for direct vulcanization adhesion with the polyamide resin in the innermost layer 102. Because this adhesive component is highly hydrophilic, the water outside the hose easily enters the rubber layer and is easily released inside the hose. As such, the permeation of the water from the outside of the hose is not sufficiently restrained. For this reason, the hose of Patent Literature 1 is not suitable for electric compressors as it is, and the water barrier properties must be further improved.
In the meanwhile, an example of hoses for transporting refrigerants, which have improved gas barrier properties of butyl rubber, is a hose recited in Patent Literature 2. In this hose, the gas barrier properties, flexibility, and processability are improved by adding polybutene and white filler to the butyl rubber of the innermost layer. However, the tensile strength is insufficient. Furthermore, because of the absence of a resin layer, the gas barrier properties of this hose are inferior to the gas barrier properties of hoses such as the hose of Patent Literature 1 having a polyamide resin layer. Moreover, because the butyl rubber significantly swells with POE lubricating oil, the hose of Patent Literature 2 in which the innermost layer is made of butyl rubber cannot be used for electric compressors as it is. The water barrier properties of the butyl rubber are not mentioned in the document.